The present invention generally relates to devices for arresting an element on a shaft. More particularly, the present invention pertains to an attachment mechanism intended for arresting a machine member, such as a pulley, a sheave, a sprocket or the like, on a cylindrical shaft.
The mounting of elements such as sheaves, sprockets or the like on a cylindrical shaft so that the element is arrested against circumferential and/or axial movements relative to the shaft can be affected in different ways. One example is to provide a keyway in the shaft and/or in the boss or hub of the machine member, and a key inserted in the keyway for preventing relative circumferential movement. However, this arresting mechanism requires a more expensive machining of the keyway in the shaft, reduces the strength of the shaft and is not well suited to being used together with relatively light and inexpensive hollow shafts.
Similar limitations can be seen with use of threaded joints as this requires thread cutting of the shaft and inner surface of the bore in the machine member.
Cylindrical shaft and hub joints can also be obtained with a press fit affected with or without the use of a pressure oil arrangement. However, with these mechanisms, it is also difficult to use hollow shafts due to large radially inwardly directed forces.
Swedish Patent Application No. 9901711-3 discloses an attachment mechanism intended for arresting a machine member having a substantially cylindrical bore on a cylindrical shaft. The bore has a larger inner diameter than the outer diameter of the shaft to provide an annular space between the machine member and the shaft. In this space is inserted a pair of elements having mating, cooperating taper surfaces facing each other, with the elements being intended at mutual displacement to change their overall radial size, thereby increasing or reducing the clamping force between the machine member and the shaft. The elements are in the form of a first thin-walled sleeve member having a smooth inner surface arranged to enclose a portion of the shaft, and a second thin-walled sleeve member having a smooth outer surface arranged to engage the bore of the machine member, with the second sleeve member enclosing the first sleeve member. The first and second sleeve members in their surfaces that face each other have a plurality of saw-tooth-shaped consecutive axially tapering sections. In addition, one of the end edges of the second sleeve member abuts against a stop provided in the machine member, and the first sleeve member projects outside the opposite end edge of the second sleeve member for being readily accessible to receive an external pushing force causing such mutual displacement between the first and second sleeve members.
This generally described attachment mechanism is able to function relatively well, but suffers from the drawback that the size relationship between the shaft and bore of the sheave is very important for allowing proper attachment to be obtained. This makes it necessary to provide a substantial number of differently sized sleeve members.
FIG. 1 shows in cross-section an attachment device similar to that described above and disclosed in Swedish patent application No. 9901711-3. In this known device, a machine member 11 is secured to a portion of a hollow shaft 10. The machine member 11 is shown only partially and is in the form of a sheave. As shown, the hollow shaft 10 has a cylindrical external peripheral surface and the machine member 11 has an inner bore of cylindrical shape, with the inner diameter of the bore in the machine member 11 exceeding the outer diameter of the shaft 10. A shoulder 12 is provided at one axial side of the bore in the machine member 11. This shoulder 12 has a diameter slightly larger than the outer diameter of the shaft 10, thereby providing a clearance so that the machine member 11 can be easily pushed up the shaft 10 to a desired arresting position. The annular space 13 formed between the inner surface of the bore in the machine member 11 and the outer peripheral surface of the shaft 10 has a certain radial dimension x. In this space is inserted the primary part of the attachment mechanism which is in the form of the two-piece sleeve 15.
This two-piece sleeve 15 includes a first or inner sleeve piece 15a having a cylindrical inner surface and an external surface provided with a continuous axially arranged series of tapering, substantially saw-tooth-shaped surface elements, in which a first surface element b tapers from a larger diameter to a smaller diameter, followed by a consecutive second surface element c connected to the first surface element b via a substantially radial wall member d so that the end of the second surface element c adjacent the narrower end of the first surface element b has substantially the same outer diameter as that of the first surface element b at its largest end, i.e. at the end remote from the second surface element c. The second surface element c is related to and connected to the consecutive next surface element e in the same manner as the relationship between the first and second surface elements b, c, with this same relationship continuing along the length of the exterior surface of the inner sleeve piece.
The second or outer sleeve piece 15xe2x80x2 of the two-piece sleeve is designed as a reverse image of the first inner sleeve piece 15a. Thus, the outer second sleeve piece 15xe2x80x2 has a cylindrical outer peripheral surface and an inner surface provided with saw-tooth-shaped surface elements that are complementary to those of the first sleeve piece 15a. The outer second sleeve piece 15xe2x80x2 is arranged to enclose the inner sleeve piece 15a, with a short section f of the inner sleeve 15a projecting axially beyond the interior of the outer second sleeve piece 15xe2x80x2 as shown in FIG. 1.
This known attachment mechanism also incorporates a ring member 16 arranged around the shaft 10 on the side of the machine member 11 facing away from the shoulder 12. This ring member 16 is provided with a number of axially extending through-holes 16a, each of which receives a bolt 17 projecting through the through-hole 16a and screwed into a corresponding one of several threaded bores 18 in the machine member 11. This ring member 16 abuts the projecting sleeve portion f of the inner sleeve 15a. By tightening the bolts 17, it is possible to axially move the inner sleeve piece 15a relative to the outer sleeve piece 15xe2x80x2 to cause the cooperating tapering surfaces of the inner and outer sleeve pieces 15a, 15xe2x80x2 to slide against each other, thereby first reaching the radial measure x of the space 13, and thereafter upon continued tightening of the bolts increasing the grip between the attachment mechanism and the shaft 10 as well as between the attachment mechanism and the interior of the machine member 11 until a firm grip is obtained in the circumferential as well as in the axial direction.
By virtue of the consecutive saw-tooth-shaped taper portions being made in an integral unit, the attachment mechanism is centered in its seat without risk of misalignment. In addition, the handling and stock-keeping of the attachment mechanism is somewhat simplified.
The known attachment mechanism described above and illustrated in FIG. 1 provides very good and reliable attachment results. However, the arresting of sheaves of various bore diameters requires stock-keeping a large variety of sizes of the attachment mechanisms. Alternatively, this requires separate manufacture for different relationships between the bore and shaft diameter.
A need thus exists for an improved attachment mechanism of the type mentioned above which is not as susceptible to the drawbacks mentioned above, and which is useful for a wide variety of sheave bore diameters with only a few different sizes
One aspect of the invention involves an attachment device mounted with respect to a machine member and a cylindrical shaft to arrest the machine member on the shaft, wherein the machine member has a tapering bore of greater diameter than the outer diameter of the shaft so that an annular space exists between the machine member and the shaft. The attachment device includes a two-part sleeve positioned in the annular space to provide a clamping force between the shaft and the machine member, with the two-part sleeve comprising first and second sleeve parts. Each of the first and second sleeve parts has mating, cooperating taper surfaces facing each other so that upon mutual displacement the first and second sleeve parts change their overall radial size. A first ring member is arranged about the shaft and forms a stop for the first sleeve part. At least one bolt is positioned in a hole in the first ring member and in a bore in the machine member to move the machine member relative to the shaft and effect the mutual displacement of the first and second sleeve parts. A second ring member is positioned between the two-part sleeve and the machine member, and has a tapered outer surface that matches the taper of the bore in the machine member. The second ring member has an inwardly projecting flange located at the axial end of the second ring member which faces away from the first ring member, with the inwardly projecting flange forming an abutment for the second sleeve part to transfer axial displacement of the machine member into the mutual displacement of the first and second sleeve parts.
Another aspect involves an attachment unit adapted to be mounted about a cylindrical shaft to arrest a machine member, provided with a tapered bore of greater diameter than a diameter of the cylindrical shaft so that an annular space exists between the shaft and the machine member, on the cylindrical shaft. The attachment unit includes a two-part sleeve adapted to be positioned in the annular space to provide a clamping force between the shaft and the machine member, with the two-part sleeve comprising an inner sleeve part and an outer sleeve part encircling the inner sleeve part. The inner sleeve part and the outer sleeve part each have a first end and a second end, with the second end of the outer sleeve part extending axially beyond the second end of the inner sleeve part. The inner sleeve part has a cylindrical inner surface and an outer surface provided with a plurality of axially arranged taper surfaces, and the outer sleeve part has a cylindrical outer surface and an inner surface provided with a plurality of axially arranged taper surfaces. The taper surfaces on the inner sleeve part face the taper surfaces on the outer sleeve part to cooperate with each other so that mutual displacement of the inner and outer sleeve parts effects a change in overall radial size of the inner and outer sleeve parts. A first ring member is positioned adjacent the first end of the inner sleeve part and forms a stop for engaging the first end of the inner sleeve part. A supporting device is adapted to axially move the machine member with respect to the shaft to effect the mutual displacement of the inner and outer sleeve parts. A second ring member has an inner surface facing the outer surface of the outer sleeve part, and is provided with a tapering outer surface and an inwardly projecting flange located adjacent the second end of the outer sleeve part to form an abutment for the second end of the outer sleeve part to transfer an axial displacement of the machine member into the mutual displacement of the inner and outer sleeve parts.
The attachment device or unit is quite advantageous in that it is useful for a wide variety of sheave bore diameters with only a few different sizes.